As is well known to those skilled in the art, it is desired to convert heavy hydrocarbons, such as those having a boiling point above about 1000.degree. F., into lighter hydrocarbons which are characterized by higher economic value. It is desirable to treat hydrocarbon feedstocks, particularly petroleum residue, to achieve other goals including hydrodesulfurization (HDS), hydrodenitrification (HDN), carbon residue reduction (CRR), and hydrodemetallation (HDM)--the latter particularly including removal of nickel compounds (HDNi) and vanadium compounds (HDV).
These processes typically employ hydrotreating catalysts with specified ranges of pores having relatively small diameters (i.e. micropores, herein defined as pores having diameters less than 250 .ANG.) and pores having relatively large diameters (i.e. macropores, herein defined as pores having diameters greater than 250 .ANG.).
U.S. patent application Ser. No. 8/019,495 (Dai et al., filed Feb. 19, 1993) discloses a catalyst composition useful in the hydroconversion of a sulfur- and metal-containing feedstock comprising an oxide of a Group VIII metal and an oxide of a Group V-IB metal and optionally phosphorus on a porous alumina support, the catalyst having a Total Surface Area of 240-310 m.sup.2 /g, a Total Pore Volume of 0.5-0.75 cc/g, and a Pore Diameter Distribution whereby 63-78% of the Total Pore Volume is present as micropores of diameter 55-115 .ANG. and 11-18% of the Total Pore Volume is present as macropores of diameter greater than 250 .ANG.. The heavy feedstocks are contacted with hydrogen and with the catalyst such that the catalyst is maintained at isothermal conditions and is exposed to a uniform quality of feed. The process of Dai et al. is particularly effective in achieving desired levels of hydroconversion of feedstock components having a boiling point greater than 1000.degree. F. to products having a boiling point less than 1000.degree. F. The instant invention is distinguished from Dai, et al. (U.S. patent application Ser. No. 8/019,495) in that Dai et al. requires a catalyst with a Pore Diameter Distribution whereby 63-78% of the Total Pore Volume is present as micropores of diameter 55-115 .ANG. and 11-18% of the Total Pore Volume is present as macropores of diameter greater than 250 .ANG., whereas, the catalysts employed in the instant invention require a Pore Diameter Distribution whereby only 50-62.8% of the Total Pore Volume is present as micropores of diameter 55-115 .ANG. and 20-30.5% of the Total Pore Volume is present as macropores of diameter greater than 250 .ANG..
U.S. Pat. No. 5,047,142 (to Texaco as assignee of Dai,et al.), discloses a catalyst composition useful in the hydroprocessing of a sulfur and metal-containing feedstock comprising an oxide of nickel or cobalt and an oxide of molybdenum on a porous alumina support in such a manner that the molybdenum gradient of the catalyst has a value of less than 6.0 and 15-30% of the nickel or cobalt is in an acid extractable form, and having a surface area of 150-210 m.sup.2 /g, a Total Pore Volume (TPV) of 0.50-0.75 cc/g, and a pore size distribution such that less than 25% TPV is in pores having diameters of less than 100 .ANG., 70.0-85.0% TPV is in pores having diameters of 100-160 .ANG. and 1.0-15.0% TPV is in pores having diameters of greater than 250 .ANG..
U.S. Pat. No. 4,941,964 (to Texaco as assignee of Dai, et al.) discloses a process for the hydrotreatment of a sulfur- and metal-containing feed which comprises contacting said feed with hydrogen and a catalyst in a manner such that the catalyst is maintained at isothermal conditions and is exposed to a uniform quality of feed, the catalyst comprising an oxide of a Group VIII metal, an oxide of a Group VI-B metal and 0-2.0 weight % of an oxide of phosphorus on a porous alumina support, and having a surface area of 150-210 m.sup.2 /g and a Total Pore Volume (TPV) of 0.50-0.75 cc/g such that 70-85% TPV is in pores having diameters of 100-160 .ANG. and 5.5-22.0% TPV is in pores having diameters of greater than 250 .ANG..
U.S. Pat. No. 4,746,419 (Peck et al.) discloses an improved hydroconversion process for the hydroconversion of heavy hydrocarbon feedstocks containing asphaltenes, metals, and sulfur compounds, which process minimizes the production of carbonaceous insoluble solids and catalyst attrition rates. Peck et al. employs a catalyst which has 0.1 to 0.3 cc/g of its pore volume in pores with diameters greater than 1,200 .ANG. and no more than 0.1 cc/g of its pore volume in pores having diameters greater than 4,000 .ANG.. The instant invention is distinguished from Peck, et al. (U.S. Pat. No. 4,746,419) in that Peck discloses only features of macropore size distribution useful for minimizing the production of carbonaceous insoluble solids and does not disclose a pore size distribution which would provide additional hydroconversion activity, whereas, the catalysts of the instant invention require a unique pore size distribution so as to provide additional hydroconversion of feedstock components having a boiling point greater than 1000.degree. F. to products having a boiling point less than 1000.degree. F. The instant invention gives improved hydroconversion activity at constant operating conditions compared to the hydroconversion activity of a commercial vacuum resid hydroconversion catalyst having a macropore size distribution which satisfies the requirements of Peck, et al. (U.S. Pat. No. 4,746,419).
U.S. Pat. No. 4,738,944 (Robinson et al.) discloses a catalyst composition useful in the hydrotreatment of hydrocarbon oils, the catalyst containing nickel and phosphorus and about 19-21.5% Mo (calculated as the oxide) on a porous refractory oxide, having a narrow pore size distribution wherein at least 10% TPV is in pores having diameters less than 70 .ANG., at least 75% TPV is in pores having diameters between 50-110 .ANG., at least 60% TPV is in pores having diameters within about 20 .ANG. above and below the average pore diameter, and at most 25% TPV, most preferably less than 10% TPV is in pores having diameters greater than 110 .ANG..
U.S. Pat. No. 4,652,545 (Lindsley et al.) discloses a catalyst composition useful in the hydroconversion of heavy oils, the catalyst containing 0.5-5% Ni or Co and 1.8-18% Mo (calculated as the oxides) on a porous alumina support, having 15-30% of the Ni or Co in an acid extractable form, and further characterized by having a Total Pore Volume (TPV) of 0.5-1.5 cc/g with a pore diameter distribution such that (i) at least 70% TPV is in pores having 80-120 .ANG. diameters, (ii) less than 0.03 cc/g of TPV is in pores having diameters of less than 80 .ANG., and (iii) 0.05-0.1 cc/g of TPV is in pores having diameters of greater than 120 .ANG..
U.S. Pat. No. 4,395,328 (Hensley, Jr. et al.) discloses a process for the hydroconversion of a hydrocarbon stream containing asphaltenes and a substantial amount of metals, comprising contacting the stream (in the presence of hydrogen) with a catalyst present in one or more fixed or ebullating beds, the catalyst comprising at least one metal which may be a Group VI-B or Group VIII metal, an oxide of phosphorus, and an alumina support, where the alumina support material initially had at least 0.8 cc/g of TPV in pores having diameters of 0-1200 .ANG., at least 0.1 cc/g of TPV is in pores having diameters of 1200-50,000 .ANG., and a surface area in the range of 140-190 m.sup.2 /g, and the support material was formed as a composite comprising alumina and one or more oxides of phosphorus into a shaped material and was thence heated with steam to increase the average pore diameter of the catalyst support material prior to impregnation with active metals. The instant invention is distinguished from Hensley, Jr., et al. (U.S. Pat. No. 4,395,328) in that Hensley, Jr., et al. require that the catalyst support be formed from a composite of alumina and one or more oxides of phosphorus prior to shaping, steam calcining and impregnating with active metals, whereas, the catalyst supports of the instant invention are made from alumina containing at most 2.5 weight percent silica and do not contain phosphorus. The catalyst supports of the instant invention are subsequently impregnated with active metals and optionally, a phosphorus component. The instant invention is further distinguished from Hensley, Jr., et al. (U.S. Pat. No. 4,395,328) in that Hensley, Jr., et al. require that the catalyst support with a relatively low surface area of 140-190 m.sup.2 /g, whereas the catalyst supports of the instant invention require higher surface areas in the range of 320-365 m.sup.2 /g.
U.S. Pat. No. 4,395,329 (Le Page et al.) discloses a hydrorefining process of a high metal-containing feedstock employing a catalyst containing alumina, a metal from group VI and a metal from the iron group, the catalyst having a Total Surface Area of 120-200 m.sup.2 /g, a Total Pore Volume of 0.8-1.2 cc/g, and a Pore Diameter Distribution whereby 0-10% of the Total Pore Volume is present as micropores of with diameters less than 100 .ANG., 35-60% of the Total Pore Volume is in pores with diameters of 100-600 .ANG., and 35-55% of the Total Pore Volume is present as macropores of diameter greater than 600 .ANG.. The instant invention is distinguished from Le Page et al. (U.S. Pat. No. 4,395,329) in that Le Page et al. requires a catalyst with a relatively low surface area of 120-200 m.sup.2 /g, whereas the catalysts of the instant invention require higher surface areas in the range of 240-320 m.sup.2 /g.
U.S. Pat. No. 4,341,625 (Tamm) discloses a process for hydrodesulfurizing a metal-containing hydrocarbon feedstock which comprises contacting the feedstock with a catalyst comprising at least one hydrogenation agent (i.e. Group VI-B or Group VIII metal, or combinations thereof) on a porous support, the catalyst being further characterized by having a TPV of 0.5-1.1 cc/g with at least 70% TPV in pores having diameters of 80-150 .ANG. and less than 3% TPV in pores having diameters greater than 1000 .ANG..
U.S. Pat. No. 4,328,127 (Angevine et al.) discloses a catalyst composition for use in the hydrodemetallation-desulfurization of residual petroleum oils, the catalyst comprising a hydrogenating component (i.e. Group VI-B or Group VIII metal, or combinations thereof) on a porous support, and being further characterized by having a TPV of 0.45-1.5 cc/g with 40-75% TPV in pores having diameters of 150-200 .ANG., and up to 5% TPV in pores having diameters of greater than 500 .ANG..
U.S. Pat. No. 4,309,278 (Sawyer) discloses a process for the hydroconversion of a hydrocarbon feedstock comprising contacting the feedstock with hydrogen and a catalyst in a fixed bed, moving bed, ebullating bed, slurry, disperse phase, or fluidized bed reactor, where the catalyst comprises a hydrogenation component (i.e. Group VI-B or Group VIII metal) on a porous support, and is further characterized by having a TPV of 1.0-2.5 cc/g with no more than 0.05-0.20 cc/g of TPV in pores having diameters of greater than 400 .ANG..
U.S. Pat. No. 4,306,965 (Hensley, Jr. et al.) discloses a process for the hydrotreatment of a hydrocarbon stream comprising contacting the stream with hydrogen and a catalyst, the catalyst comprising chromium, molybdenum, and at least one Group VIII metal on a porous support, and further characterized by having a TPV of 0.4-0.8 cc/g with 0-50% TPV in pores having diameters smaller than 50 .ANG., 30-80% TPV in pores having diameters of 50-100 .ANG., 0-50% TPV in pores having diameters of 100-150 .ANG., and 0-20% TPV in pores having diameters greater than 150 .ANG..
U.S. Pat. No. 4,297,242 (Hensley, Jr. et al.) discloses a 2-stage process for the catalytic hydrotreatment of hydrocarbon streams containing metal and sulfur compounds, the process comprising: (i) first contacting the feedstock with hydrogen and a demetallation catalyst comprising a Group VI-B and/or Group VIII metal; and (ii) thereafter reacting the effluent with a catalyst consisting essentially of at least one Group VI-B metal on a porous support, and having a TPV of 0.4-0.9 cc/g and a pore size distribution such that pores having diameters of 50-80 .ANG. constitute less than 40% TPV, pores having diameters of 80-100 .ANG. constitute 15-65% TPV, pores having diameters of 100-130 .ANG. constitute 10-50% TPV, and pores having diameters of greater than 130 .ANG. less than 15% TPV.
U.S. Pat. No. 4,089,774 (Oleck et al.) discloses a process for the demetallation and desulfurization of a hydrocarbon oil comprising contacting the oil with hydrogen and a catalyst, the catalyst comprising a Group VI-B metal and an iron group metal (i.e. iron, cobalt, or nickel) on a porous support, and having a surface area of 125-210 m.sup.2 /g and TPV of 0.4-0.65 cc/g with at least 10% TPV in pores having diameters less than 30 .ANG., at least 50% of pore volume accessible to mercury being in pores having diameters of 30-150 .ANG., and at least 16.6% of pores accessible to mercury being in pores having diameters greater than 300 .ANG.. The instant invention is distinguished from Oleck et al. (U.S. Pat. No. 4,089,774) in that Oleck et al. requires a catalyst with a relatively low surface area of 125-210 m.sup.2 /g, whereas the catalysts of the instant invention require higher surface areas in the range of 240-320 m.sup.2 /g.
U.S. Pat. No. 4,082,695 (Rosinski et al.) discloses a catalyst for use in the demetallation and desulfurization of petroleum oils, the catalyst comprising a hydrogenating component (i.e. cobalt and molybdenum) on a porous support, and having a surface area of 110-150 m.sup.2 /g and a pore size distribution such that at least 60% of TPV is in pores having diameters of 100-200 .ANG. and not less than 5% TPV is in pores having diameters greater than 500 .ANG..
U.S. Pat. No. 4,066,574 (Tamm) discloses a catalyst composition useful in the hydrodesulfurization of a hydrocarbon feedstock containing organometallic compounds, the catalyst comprising Group VI-B and Group VIII metal components on a porous support, and having a TPV of 0.5-1.1 cc/g with a pore diameter distribution such that at least 70% TPV is in pores of diameters of 80-150 .ANG. and less than 3% TPV is in pores having diameters greater than 1000 .ANG..
U.S. pat. No. 4,051,021 (Hamner) discloses a catalytic process for the hydrodesulfurization of a hydrocarbon feed which comprises contacting the feed with hydrogen and a catalyst, the catalyst comprising a Group VI-B and Group VIII metal on a porous support, and having a TPV of 0.3-1.0 cc/g with a pore diameter distribution such that greater than 50% TPV is in pores of diameters of 70-160 .ANG., and pores having diameters below 70 .ANG. and above 160 .ANG. are minimized.
U.S. Pat. No. 4,048,060 (Riley) discloses a two-stage process for hydrodesulfurizing a heavy hydrocarbon feed which comprises: (i) contacting the feed with hydrogen and a first catalyst to produce a first hydrodesulfurized hydrocarbon product, the first catalyst comprising a Group VI-B and Group VIII metal on a porous support and having a mean pore diameter of 30-60 .ANG.; and (ii) contacting the first hydrodesulfurized hydrocarbon product with hydrogen and a second catalyst under hydrodesulfurization conditions, the second catalyst comprising a Group VI-B and Group VIII metal on a porous support and being further characterized by having a TPV of 0.45-1.50 cc/g with 0-0.5 cc/g of TPV in pores having diameters greater than 200 .ANG., 0-0.05 cc/g of TPV in pores having diameters below 120 .ANG., and at least 75% TPV in pores having diameters .+-.10 .ANG. of a mean pore diameter of 140-190 .ANG..
U.S. pat. No. 3,876,523 (Rosinski et al.) discloses a process for the demetallizing and desulfurizing of residual petroleum oil comprising contacting the oil with hydrogen and a catalyst, the catalyst comprising a Group VI-B and Group VIII metal on a porous support and having a pore size distribution such that greater than 60% TPV is in pores having diameters of 100-200 .ANG., at least 5% TPV is in pores having diameters greater than 500 .ANG., and 10% TPV or less is in pores having diameters less than 40 .ANG., and the surface area of the catalyst is 40-150 m.sup.2 /g.
U.S. Pat. No. 3,770,617 (Riley et al.) discloses a process for the desulfurization of a petroleum hydrocarbon feed comprising contacting the feed with hydrogen and a catalyst, the catalyst comprising a Group VI-B or Group VIII metal on a porous support and having greater than 50% TPV in pores of 30-80 .ANG., less than 4% TPV in pores having diameters 200-2000 .ANG., and at least 3% TPV in pores having diameters greater than 2000 .ANG..
U.S. pat. No. 3,692,698 (Riley et al.) discloses a catalyst useful in hydroprocessing of heavy feed stocks, the catalyst comprising a mixture of Group VI-B and Group VIII metals on a porous support and having a pore size distribution such that a major portion of its TPV is in pores of diameters ranging from 30-80 .ANG., less than 4% TPV is in pores of diameters of 200-2000 .ANG., and at least 3% TPV is in pores of diameters greater than 2000 .ANG..
Early petroleum distillate hydrotreating catalysts generally were monomodal catalysts with very small micropore diameters (less than say 100 .ANG.) and rather broad pore size distributions. First generation petroleum resid hydrotreating catalysts were developed by introducing a large amount of macroporosity into a distillate hydrotreating catalyst pore structure to overcome the diffusion resistance of large molecules. Such catalysts, which are considered fully bimodal HDS/HDM catalysts, are typified by U.S. Pat. Nos. 4,746,419, 4,395,328, 4,395,329, and 4,089,774 supra.
Another approach to developing improved catalysts for petroleum resid processing has involved enlarging the micropore diameters of essentially monomodal catalysts (having no significant macroporosities) to overcome the above described diffusion limitations. Essentially monomodal catalysts with small micropore diameters and low macroporosities designed for improved petroleum resid HDS include those disclosed in U.S. Pat. Nos. 4,738,944; 4,652,545; 4,341,625; 4,309,378; 4,306,965; 4,297,242; 4,066,574; 4,051,021; 4,048,060 (1st stage catalyst); 3,770,617; and 3,692,698; supra. Essentially monomodal catalysts with larger micropore diameters and low macroporosities designed for improved petroleum resid HDM include those disclosed in U.S. Pat. Nos. 4,328,127; 4,309,278; 4,082,695; 4,048,060 (2nd stage catalyst); and 3,876,523, supra.
A recent approach to developing improved catalysts for petroleum resid processing has involved the use of catalysts having micropore diameters intermediate between the above described monomodal HDS and HDM catalysts, as well as sufficient macroporosities so as to overcome the diffusion limitations for petroleum bottoms HDS (i.e., sulfur removal from hydrocarbon product of a hydrotreated petroleum resid having a boiling point greater than 1000.degree. F.) but limited macroporosities to limit poisoning of the interiors of the catalyst particles. Catalysts with micropore diameters intermediate between the above described monomodal HDS and HDM catalysts with limited macroporosities include those of U.S. Pat. Nos. 4,941,964 and 5,047,142 supra.
However, none of the above-identified catalyst types, which improve hydrodesulfurization and/or hydrodemetallation, have been found to be effective for achieving improved levels of hydroconversion of feedstocks components having a boiling point greater than 1000.degree. F. to products having a boiling point less than 1000.degree. F. In particular, none of the above-identified catalyst types have been found to be effective for achieving improved levels of hydroconversion when operated under the same process conditions as those employed with first generation petroleum resid hydrotreating catalysts. Undesirable low levels of hydroconversion represent a problem which is particularly acute for those refiners who operate vacuum resid hydroprocessing units at their maximum heat and/or temperature limits. Such limits often exist when refiners are operating at maximum charge rates.
A recent approach to developing such catalysts for the improved hydroconversion of feedstock components having a boiling point greater than 1000.degree. F. to products having a boiling point less than 1000.degree. F. has involved the use of catalysts having micropores intermediate between the abovedescribed monomodal HDS and HDM catalysts with rather more pore volumes in the HDS type of range and with sufficient macroporosities so as to overcome the diffusion limitations for conversion of feedstock components having boiling points greater than 1000.degree. F. into products having boiling points less than 1000.degree. F. but limited macroporosities so as to limit poisoning of the interiors of the catalyst particles. Such catalysts are described in U.S. patent application Ser. No. 8/019,415 supra.
It is another feature of the prior art, particularly petroleum resid processing prior art, that it has not heretofore always been possible to carry out the desirable levels of hydroconversion of such feedstocks to attain desirable results as measured by conversion without the undesirable formation of sediment.
The charge to a hydroconversion process is typically characterized by a very low sediment content of 0.01 weight percent (w %) maximum. Sediment is typically measured by testing a sample by the Shell Hot Filtration Solids Test (SHFST). See Jour. Inst. Pet. (1951) 37 pages 596-604 Van Kerknoort et al.--incorporated herein by reference. Typical prior art hydroprocessing processes commonly yield Shell Hot Filtration Solids of above about 0.19 w % and as high as about 1 w % in the 650.degree. F.+ product recovered from the bottoms flash drum (BFD). Production of large amounts of sediment is undesirable in that it results in deposition in downstream units which in due course must be removed. This of course requires that the unit be shut down for an undesirable long period of time. Sediment is also undesirable in the products because it deposits on and inside various pieces of equipment downstream of the hydroprocessing unit and interferes with proper functioning of e.g. pumps, heat exchangers, fractionating towers, etc.
Undesirable high levels of sediment formation, however, are not usually experienced by those refiners who operate vacuum resid hydroprocessing units at or near their maximum heat and feedstock charge rates. Such units are generally operating at moderate conversion levels of feedstock components having boiling points greater than 1000.degree. F. into products having boiling points less than 1000.degree. F. (say, 40-65 volume percent--vol %--conversion) and at relatively low values of sediment. Sediment formation is still of concern, however, in processes such as that of the instant invention, employing catalysts to achieve improved levels of hydroconversion.
We have found it very useful to employ the IP 375/86 test method for the determination of total sediment. The test method is also described in ASTM Designation D 4870-92--incorporated herein by reference. The IP 375/86 method was designed for the determination of total sediment in residual fuels and is very suitable for the determination of total sediment in our 650.degree. F.+ boiling point product. The 650.degree. F.+ boiling point product can be directly tested for total sediment which is designated as the "Existent IP Sediment value." We have found that the Existent IP Sediment Test gives essentially equivalent test results as the Shell Hot Filtration Solids Test described above.
We have noted, however, that even 650.degree. F.+ boiling point products which give low Existent IP Sediment values, may produce additional sediment upon storage. Thus, we have developed a more severe test for sediment. In this modified test, 50 grams of 650.degree. F.+ boiling point product are heated to about 90.degree. C. and mixed with about 5 milliliters of reagent grade hexadecane. The mixture is aged for about one hour at about 100.degree. C. The resultant sediment is then measured by the IP 375/86 test method. The values obtained from this modified test are designated the "Accelerated IP Sediment values."
As it is recommended that the IP 375/86 test method be restricted to samples containing less than or equal to about 0.4 to 0.5 w % sediment, we reduce sample size when high sediment values are observed. This leads to fairly reproducible values for even those samples with very large sediment contents.
It is an object of this invention to provide a process for hydroconverting a charge hydrocarbon feed, particularly, to hydroconvert feedstock components having boiling points greater than 1000.degree. F. into products having boiling points less than 1000.degree. F. It is a second object of this invention to provide improved conversion at low Existent IP sediment values in the 650.degree. F.+ boiling point product. Other objects will be apparent to those skilled in the art.